How to make a bronze material in Cycles?
Here's what I came up with using procedural textures:



I would use dirty vertex colors in 3D view > header > Paint while in Vertex paint mode to add some dirt to the corners:



You can then use this in your node setup via an Attribute node, with the name set to the name of the vertex color layer (Col by default):





You could more than likely get a better result more easily by using image textures.

I'd also recommend this tutorial, which has some great examples (and a free image texture).